Making malleable-iron castings



: castings is to raise Patented July 19, 1927.

UNITED STATES PATENT OFFICE. v

HARRY A. SCHWARTZ, OF CLEVELAND HEIGHTS, OHIO, ASSIGNOR, BY MESNE ASSIGN- MEN'IS, TO NATIONAL MALLEABLE AND STEEL CASTINGS COMPANY, OF CLEVE- LAND, OHIO, A. CORPORATION OF OHIO.

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No Drawing. Application filed February 5, 1923, Serial No. 617,163. Renewed December 7, 1926.

, In the manufacture of malleable iron castings it is customary to have silicon present in the iron before casting so that, n the subsequent malleabilizing operation, it may as- 5 sist the decomposition or breaking up of the cementite in the iron. After casting and Whilethe casting is cooling the presence of too much silicon, however, causes the precipitation, during or just after freezing, of

1 a percentage of the carbon in the flaky form normally found in grey iron castings and renders the castings worthless for conversion into malleable iron, and owing to this action the amount of silicon present or to 5 be added must be regulated with very great care. I have found that additions of small proportions of graphitization accelerators such as uranium and nickel, and particular- 1y of titanium and aluminum, to 1ron containing an inappreciable percentage of silicon greatly accelerate the annealing cycle of malleable iron, acting in much the same way as larger amounts of silicon, but with-- out the deleterious effects of silicon. 1

I have In carrying out my invention 0 found that iron eontainin no substantial percentage of silicon an approximately .10.15% of titanium or aluminum (these amounts being those contained in castings 80 after they have been malleabilized) maybe cast without precipitating the carbon, and when annealed graphitizes as completely and more satisfactorily than malleable iron of normal analysis which contains substanas tially .60.7 5% of silicon and no titanium or aluminum. The addition of suitably larger amounts would still further promote ease of annealing. Similar additions in properly reduced amount can be made to metal having the silicon content usual n malleable iron. Such additions will similarly benefit the metal with respect to its annealing properties, resulting either in a marked reduction of the time required for an anneal or in a reduction (amounting to as much as 25% or more) in the amount of material requiring further treatment to remedy the defects of the first anneal.

The effect of silicon in iron formalleable the critical point above which carbon is soluble and to 'lower the solubility of free carbon in solid iron at all temperatures above the critical point just mentioned. Silicon thus acts by decreasing the solubility of carbon in the iron and renders graphitization during annealing at a given temperature more rapid and complete, but by reason of its completeness there is danger of precipitation of carbon while cooling in the mold, which is ordinarily known as primary graphitization. Neither titanium nor aluminum, on the other hand, so far as I have observed, has any appreciable effect on the critical point of the alloy and each appears to increase instead of decrease the solubility of carbon. So far as I have observed, other metals in addition to titanium and aluminum, such as nickel and uranium, havethe power of increasing the rate of graphitization at annealing temperatures without so far lowering the solubility of carbon and increasing the rate of graphitization near the melting points as to roduce precipitation of the carbon in the orm of graphite flakes.

My invention is particularly adapted for use in making malleable castings with com paratively heavy sections, since the slow cooling of such castings in the casting 0 eration, because of their thicksection's, ten s to permit the precipitation of the carbon in flaky form if the castings contain too high a percentage of silicon. A result of using such graphitization accelerators as titanium and aluminum is to shorten the annealing cycle and'therefore decrease the time durin which the surface of the castings is exposed to the decarbonizing effects of air or of the packing material which is in contact with such surface, so that the thickness of the ferrite skin on the castings formed by such exposure is lessened by the shortening of the time of exposure. As this ferrite skin is more diflicult to machine than the material underneath, a definite improvement in machining qualities is thus achieved.

The terms and expressions which I have em loyed are used as terms of description an not of limitation, and I have no intention, in the use of such terms and ex ressions, of excluding any equivalents o the features shown and described, or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed, it being understood that by the use of the term graphitization accelerators I include such elements as assist in the graphitization of the metal during annealing.

What I claim is: a

1. The process of making malleable iron castings containing an inappreciable percentage of silicon which comprises adding a graphitization accelerator to the iron, casting the metal Without precipitating a substantial proportion of the carbon, annealing the casting and thereby precipitating the carbon, in the form of small particles.

2. The process of makin malleable iron castings which comprises adilin a graphitization accelerator other than silicon to the iron before casting, casting the metal without substantial precipitation of the carbon, annealing the casting and thereby precipitating substantially all of the carbon in the form of small particles.

3. The process of makin malleable iron castings which comprises a ding a graphitizati'on accelerator to the iron, castin the metal and annealing the casting, the said accelerator having a neutral efiect on the formation of aphite during casting but act- 'ing to acce crate the decomposition of the grain structure of the metal and assist in the precipitation of the carbon into the form of small graphite particles during annealing.

4. The rocess of making malleable iron castings w 'ch comprises adding a graphitization accelerator to the iron Without materially aifecting the critical point of the metal and at the same time not materially affecting the solubility of the carbon, casting the metal without substantial precipitation of the carbon and annealin the casting, and thereby recipitating a su stantial proportion of t e carbon. I

5. The process of making malleable iron castings which comprises adding a small ercentage of titanium or aluminum to the iron, castin the metal and annealing the casting, an thereby eflecting graphitization 0 the casting during annealing.

6. The rocess of makin malleable iron castings w ich comprises a ding from .10 to .15 per cent of titanium or aluminum to the iron, casting the metal and annealing the castin and thereby efiecting graphitization 0 the casting during annealin HARRY A. SCHW RTZ. 

